Workers are reminded to be careful as they work excavating down under ground approximately 65 feet to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

Workers are reminded to be careful as they work excavating down under ground approximately 65 feet to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

Photo: Lacy Atkins, The Chronicle

Workers are reminded to be careful as they work excavating down... Photo-3930238.67016 - StamfordAdvocate

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Workers Dwayne Jackson, center and Ryan Lewis connect the struts across the excavation site approximately 65 feet under ground as to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif. less

Workers Dwayne Jackson, center and Ryan Lewis connect the struts across the excavation site approximately 65 feet under ground as to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, ... more

Workers climb along the struts to make sure the construction is properly secure under the ground where the excavation is being done down to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif. less

Workers climb along the struts to make sure the construction is properly secure under the ground where the excavation is being done down to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San ... more

Photo: Lacy Atkins, The Chronicle

Workers climb along the struts to make sure the construction is... Photo-3930235.67016 - StamfordAdvocate

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Workers excavate on a 7 year project of building the new Transbay Terminal site, Monday Dec. 17, 2012.

Workers excavate on a 7 year project of building the new Transbay Terminal site, Monday Dec. 17, 2012.

Photo: Lacy Atkins, The Chronicle

Workers excavate on a 7 year project of building the new Transbay... Photo-3930233.67016 - StamfordAdvocate

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Workers excavate between 2nd and 4th street as they work aon a 7 years project of building the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

Workers excavate between 2nd and 4th street as they work aon a 7 years project of building the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

Photo: Lacy Atkins, The Chronicle

Workers excavate between 2nd and 4th street as they work aon a 7... Photo-3930231.67016 - StamfordAdvocate

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J.C. Daughrity welds the struts as workers excavate under ground approximately 65 feet to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

J.C. Daughrity welds the struts as workers excavate under ground approximately 65 feet to build the new Transbay Terminal site, Monday Dec. 17, 2012, in San Francisco, Calif.

Workers removing old piles to build the new Transbay Terminal... Photo-3930229.67016 - StamfordAdvocate

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Crane operator Brandon Valasik (not shown) unearthed parts of the remains of a wooly mammoth with his crane (lower center) seen in the work area Wednesday, September 12, 2012, in San Francisco, Calif., at the site of the new Transbay Terminal. less

Crane operator Brandon Valasik (not shown) unearthed parts of the remains of a wooly mammoth with his crane (lower center) seen in the work area Wednesday, September 12, 2012, in San Francisco, Calif., at the ... more

Geologist Jim Allen speaks to the media on Wednesday, September 12, 2012, displaying wooly mammoth remains after construction crews digging on the site of the Transbay Terminal in San Francisco, Calif., have unearthed the remains. less

Geologist Jim Allen speaks to the media on Wednesday, September 12, 2012, displaying wooly mammoth remains after construction crews digging on the site of the Transbay Terminal in San Francisco, Calif., have ... more

Geologist Jim Allen speaks to the media on Wednesday, September 12, 2012, displaying wooly mammoth remains after construction crews digging on the site of the Transbay Terminal in San Francisco, Calif., have unearthed the remains. less

Geologist Jim Allen speaks to the media on Wednesday, September 12, 2012, displaying wooly mammoth remains after construction crews digging on the site of the Transbay Terminal in San Francisco, Calif., have ... more

Salvaged pieces of the old Transbay Terminal are now piled on the corner of Mission St and Fremont St in San Francisco, Calif. in preparation for artist Tim Hawkinson's 40-foot-tall sculpture. The sculpture will stand on the same corner at the front of the new Terminal. Photographed on Friday, June 3, 2011. less

Salvaged pieces of the old Transbay Terminal are now piled on the corner of Mission St and Fremont St in San Francisco, Calif. in preparation for artist Tim Hawkinson's 40-foot-tall sculpture. The sculpture ... more

Photo: Audrey Whitmeyer-Weathers, The Chronicle

Salvaged pieces of the old Transbay Terminal are now piled on the... Photo-1895153.67016 - StamfordAdvocate

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The demolition of the Transbay Terminal at Mission and 1st Streets in downtown San Francisco, Calif., continues on Friday Jan. 7, 2011.

The demolition of the Transbay Terminal at Mission and 1st Streets in downtown San Francisco, Calif., continues on Friday Jan. 7, 2011.

Photo: Michael Macor, The Chronicle

The demolition of the Transbay Terminal at Mission and 1st Streets... Photo-2066341.67016 - StamfordAdvocate

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After 70-plus years of service, Joy Daniels sweeps up debris as construction crews work to demolish the Transbay Terminal on Wednesday Dec. 1, 2010 in San Francisco, Calif.

After 70-plus years of service, Joy Daniels sweeps up debris as construction crews work to demolish the Transbay Terminal on Wednesday Dec. 1, 2010 in San Francisco, Calif.